Almost all of the current CMC models select conversational history based on a heuristic of considering \(k\)  immediate turns, often decided by performance such as BiDAF++ [1]}, [2]}, SDNet [3]}, BiDAF++ w/ 2-ctx [4]} use last two turns as including the third turn degrades performance. History Attention Mechanism (HAM) based model ham uses a dynamic history selection policy by attending over contextualized representations of all the previous history turns at word-level or sequence-level and combining with current turn's representation as shown in Fig. REF .
